diff --git a/backend/src/api-keys/api-keys.controller.ts b/backend/src/api-keys/api-keys.controller.ts
index 2d65beb..0c75958 100644
--- a/backend/src/api-keys/api-keys.controller.ts
+++ b/backend/src/api-keys/api-keys.controller.ts
@@ -11,6 +11,7 @@ import {
 import { AuthGuard } from "../auth/guards/auth.guard";
 import type { AuthenticatedRequest } from "../common/interfaces/request.interface";
 import { ApiKeysService } from "./api-keys.service";
+import { CreateApiKeyDto } from "./dto/create-api-key.dto";
 
 @Controller("api-keys")
 @UseGuards(AuthGuard)
@@ -20,13 +21,12 @@ export class ApiKeysController {
 	@Post()
 	create(
 		@Req() req: AuthenticatedRequest,
-		@Body("name") name: string,
-		@Body("expiresAt") expiresAt?: string,
+		@Body() createApiKeyDto: CreateApiKeyDto,
 	) {
 		return this.apiKeysService.create(
 			req.user.sub,
-			name,
-			expiresAt ? new Date(expiresAt) : undefined,
+			createApiKeyDto.name,
+			createApiKeyDto.expiresAt ? new Date(createApiKeyDto.expiresAt) : undefined,
 		);
 	}
 
diff --git a/backend/src/api-keys/dto/create-api-key.dto.ts b/backend/src/api-keys/dto/create-api-key.dto.ts
new file mode 100644
index 0000000..91601a6
--- /dev/null
+++ b/backend/src/api-keys/dto/create-api-key.dto.ts
@@ -0,0 +1,12 @@
+import { IsDateString, IsNotEmpty, IsOptional, IsString, MaxLength } from "class-validator";
+
+export class CreateApiKeyDto {
+	@IsString()
+	@IsNotEmpty()
+	@MaxLength(128)
+	name!: string;
+
+	@IsOptional()
+	@IsDateString()
+	expiresAt?: string;
+}
diff --git a/backend/src/categories/dto/create-category.dto.ts b/backend/src/categories/dto/create-category.dto.ts
index 52e0884..1459f00 100644
--- a/backend/src/categories/dto/create-category.dto.ts
+++ b/backend/src/categories/dto/create-category.dto.ts
@@ -1,15 +1,18 @@
-import { IsNotEmpty, IsOptional, IsString } from "class-validator";
+import { IsNotEmpty, IsOptional, IsString, MaxLength } from "class-validator";
 
 export class CreateCategoryDto {
 	@IsString()
 	@IsNotEmpty()
+	@MaxLength(64)
 	name!: string;
 
 	@IsOptional()
 	@IsString()
+	@MaxLength(255)
 	description?: string;
 
 	@IsOptional()
 	@IsString()
+	@MaxLength(512)
 	iconUrl?: string;
 }
diff --git a/backend/src/contents/dto/create-content.dto.ts b/backend/src/contents/dto/create-content.dto.ts
index 096601e..7c0aa92 100644
--- a/backend/src/contents/dto/create-content.dto.ts
+++ b/backend/src/contents/dto/create-content.dto.ts
@@ -6,6 +6,7 @@ import {
 	IsOptional,
 	IsString,
 	IsUUID,
+	MaxLength,
 } from "class-validator";
 
 export enum ContentType {
@@ -19,14 +20,17 @@ export class CreateContentDto {
 
 	@IsString()
 	@IsNotEmpty()
+	@MaxLength(255)
 	title!: string;
 
 	@IsString()
 	@IsNotEmpty()
+	@MaxLength(512)
 	storageKey!: string;
 
 	@IsString()
 	@IsNotEmpty()
+	@MaxLength(128)
 	mimeType!: string;
 
 	@IsInt()
@@ -39,5 +43,6 @@ export class CreateContentDto {
 	@IsOptional()
 	@IsArray()
 	@IsString({ each: true })
+	@MaxLength(64, { each: true })
 	tags?: string[];
 }
diff --git a/backend/src/contents/dto/upload-content.dto.ts b/backend/src/contents/dto/upload-content.dto.ts
index ca4b284..a67c3d7 100644
--- a/backend/src/contents/dto/upload-content.dto.ts
+++ b/backend/src/contents/dto/upload-content.dto.ts
@@ -4,6 +4,7 @@ import {
 	IsOptional,
 	IsString,
 	IsUUID,
+	MaxLength,
 } from "class-validator";
 import { ContentType } from "./create-content.dto";
 
@@ -13,6 +14,7 @@ export class UploadContentDto {
 
 	@IsString()
 	@IsNotEmpty()
+	@MaxLength(255)
 	title!: string;
 
 	@IsOptional()
@@ -20,6 +22,8 @@ export class UploadContentDto {
 	categoryId?: string;
 
 	@IsOptional()
+	@IsArray()
 	@IsString({ each: true })
+	@MaxLength(64, { each: true })
 	tags?: string[];
 }
diff --git a/backend/src/reports/dto/create-report.dto.ts b/backend/src/reports/dto/create-report.dto.ts
index 4a5284d..53a9bae 100644
--- a/backend/src/reports/dto/create-report.dto.ts
+++ b/backend/src/reports/dto/create-report.dto.ts
@@ -1,4 +1,4 @@
-import { IsEnum, IsOptional, IsString, IsUUID } from "class-validator";
+import { IsEnum, IsOptional, IsString, IsUUID, MaxLength } from "class-validator";
 
 export enum ReportReason {
 	INAPPROPRIATE = "inappropriate",
@@ -21,5 +21,6 @@ export class CreateReportDto {
 
 	@IsOptional()
 	@IsString()
+	@MaxLength(1000)
 	description?: string;
 }
diff --git a/backend/src/users/dto/update-consent.dto.ts b/backend/src/users/dto/update-consent.dto.ts
index 3456a81..aa97e7e 100644
--- a/backend/src/users/dto/update-consent.dto.ts
+++ b/backend/src/users/dto/update-consent.dto.ts
@@ -1,11 +1,13 @@
-import { IsNotEmpty, IsString } from "class-validator";
+import { IsNotEmpty, IsString, MaxLength } from "class-validator";
 
 export class UpdateConsentDto {
 	@IsString()
 	@IsNotEmpty()
+	@MaxLength(16)
 	termsVersion!: string;
 
 	@IsString()
 	@IsNotEmpty()
+	@MaxLength(16)
 	privacyVersion!: string;
 }